In general, a hydraulic excavator as a construction machine comprises an automotive lower traveling structure, an upper revolving structure that is rotatably mounted on the lower traveling structure, and a front device that is liftably mounted in a front part of the upper revolving structure. The front device is configured of a boom, an arm, a bucket and a plurality of hydraulic actuators composed of a boom cylinder, an arm cylinder and a bucket cylinder that drive the above components respectively. The front device actuates each of the hydraulic actuators to perform an excavating operation of earth and sand.
The upper revolving structure is provided with a revolving frame that is configured as a support structure, a counterweight that is positioned in a rear side of the revolving frame to act as a weight balance to the front device, an engine that is disposed on the revolving frame in a laterally-facing state to be positioned in a front side to the counterweight, a heat exchanger that is provided to be positioned in one side of the engine in a length direction, a cab that is provided on the revolving frame to be positioned in a front side to the heat exchanger, a NOx purifying device that is mounted in an exhaust pipe of the engine and is provided with a urea selective reduction catalyst for removing nitrogen oxides in an exhaust gas by injection of urea water from a urea water injection valve, and a urea water tank that reserves urea solution therein for supply to the urea water injection valve in the NOx purifying device.
Further, the revolving frame includes a flat bottom plate, left and right vertical plates that are provided vertically on the bottom plate at an interval in a left-right direction to extend in a front-rear direction, a plurality of extension beams that extend in the left-right direction from the bottom plate and the respective vertical plates, and a left side frame and a right side frame that are mounted in front ends of the respective extension beams to extend in the front-rear direction in outside positions of the bottom plate in the left-right direction (Patent Document 1).